1. Technical Field
The present invention relates to a semiconductor pressure sensor, a method for producing the semiconductor pressure sensor, a semiconductor device, and an electronic apparatus.
2. Related Art
Recently, in the semiconductor industry, a micro electro-mechanical system (MEMS) has become increasingly fused with IC devices to accelerate development of various multifunctional semiconductor devices. Among the semiconductor devices, particularly, acceleration sensors, gyro sensors, resonators such as timing devices have been vigorously developed. On the other hand, there are still many problems in fusion and integration of the MEMS devices and complementary metal oxide semiconductor (CMOS) devices, so that various technological solutions are being explored to solve the problems.
Conventional pressure sensors, which are used to detect pressure, are generally of capacitance type, piezo-resistance type, piezoelectric type, and the like. Among them, piezo-resistance type pressure sensors are dominantly used (e.g. See JP-A-1995-027643).
As an example of the capacitance type pressure sensors, FIG. 17 shows a pressure sensor 100 that includes a diaphragm 101 having a predetermined gap. The diaphragm 101 is movable by a pressure difference to detect capacitance changes. Accordingly, power consumption in operation is small, so that the capacitance type pressure sensors are used for a purpose of power consumption reduction. However, such a type of pressure sensor has a low sensitivity of detection. In order to maintain detection sensitivity over a certain level, the diaphragm 101 needs to be made larger, which makes a structure of the sensor more complicated. Thus, for example, in the field of the MEMS as mentioned above, it is difficult to integrate the capacitance type pressure sensor 100 of FIG. 17A with a CMOS circuit or the like detecting pressure applied to the sensor.
Examples of the piezo-resistance type pressure sensor include pressure sensors 110 and 120 shown in FIGS. 17B and 17C. In those sensors, when a bridge resistance 112 on each of semiconductor thin films 111 and 121 receives pressure to cause distortion, a resistance value change is converted into a voltage to be detected. Such a pressure sensor is highly sensitive and can be easily integrated with a CMOS circuit or the like when applied in the field of the MEMS. However, the piezo resistance type pressure sensors 110 and 120, which require allowing a constant electric current to continue to pass through the bridge resistance 112, are not desirable in terms of power consumption reduction. In particular, to ensure improvement of performance accuracy in a high-temperature range, a constant current circuit or the like is additionally needed, thereby resulting in a further increase in power consumption.
The piezoelectric type pressure sensor detects a voltage displacement occurring, for example, when a piezoelectric film on a diaphragm formed of a thinned silicon substrate is distorted by pressure applied. Consequently, the sensor achieves low power consumption and can be easily integrated with a CMOS circuit or the like in applications of the MEMS field. However, conventional piezoelectric pressure sensors have a low sensitivity in pressure detection and particularly cannot be used for purposes of detection of minute pressure changes.
Therefore, there has been a demand for a semiconductor pressure sensor that can facilitate integration with a semiconductor circuit such as a CMOS circuit, can reduce power consumption, and can exhibit a high sensitivity in pressure detection.